1. Field of the Invention
The invention relates to an apparatus for drying tobacco and more particularly relates to an apparatus for drying tobacco under relatively high humidity drying conditions.
2. Brief Description of the Prior Art
It is common practice in the manufacture of cigarettes to cut tobacco, which includes both lamina and stems, to a particle size which is appropriate in the manufacturing of cigarette products. In the processing of the tobacco prior to the cutting or shattering, the moisture content of the tobacco is generally increased in order to minimize shattering of the tobacco particles during the cutting step, and also provides a material of a more uniform particle size. As the processing of the tobacco continues, it is necessary to reduce this moisture content prior to the formation of a cigarette rod which is subsequently cut to prescribed lengths and made into a cigarette product.
In the drying of the previously cut tobacco, the initial moisture content usually ranges from about 15 to 35 percent for the lamina, and from about 20 to 60 percent for the stem. This tobacco is dried in the presence, generally, of hot air until the moisture is in the range of from about 12 to 15 percent. Several devices are known in the prior art and two examples of drying cut tobacco are disclosed in U.S. Pat. No. 3,357,436 and U.S. Pat. No. 4,167,191.
In recent years, it has become a widespread practice in the tobacco industry to expand or "puff" tobacco prior to incorporation into a cigarette product. This expansion or "puffing" leads to better economics as well as a lowering of the tar and nicotine in the final product. Many different techniques are described and known in the prior art for expanding tobacco, such as impregnation of the tobacco with water, an organic liquid, carbon dioxide, or ammonia, and then subjecting the impregnated tobacco to temperatures or pressures sufficient to then liberate the impregnant from the tobacco. However, in many of the drying techniques utilized for expanding the tobacco, many of the advantages attributed to the expansion technique are lost because of the shrinking during the drying process. Thus, an apparatus which may be utilized to dry expanded tobacco wherein the shrinkage does not occur or is minimized, is of substantial benefit in the processing of expanded tobacco particles.